High impact antenna



Oct. 13, 1970 JAMES E. WEBB ADMINISTRATOR OF THE NATIONAL AERONAUTICSAND SPACE ADMINISTRATION HIGH IMPACT ANTENNA 2 Sneets-Sheet 1 Filed Jan.30, 1968 FIG.

FIG.4

INXQEMI'OR. KENNETH E. WOO

PLANE OF SYMMETRY Q151 1 ATTORNEYS Oct. 13, 1970 JAMES E. WEBB 3,534,376

ADMINISTRATOR OF THE NATIONAL AERONAUTICS AND SPACE ADMINISTRATION HIGHIMPACT ANTENNA ATTORNEYS United States Patent 3,534,376 HIGH IMPACTANTENNA James E. Webb, Administrator of the National Aeronautics andSpace Administration, with respect to an invention of Kenneth E. Woo,South Pasadena, Calif.

Filed Jan. 30, 1968, Ser. No. 701,767 Int. Cl. HOlq 13/02 US. Cl.343--786 Claims ABSTRACT OF THE DISCLOSURE A high impact antenna isdisclosed which consists of a cup, whose open end defines the antennasradiating aperture. A probe, which is energized with microwave energy,is positioned within the cup, parallel to the cups shorted end at aselected distance therefrom and at an angle with respect to the cupsside walls to excite modes therein, which radiate outwardly through theopen end at a selected polarization. Dielectric material fills the cupto support the probe, as well as strengthen the side walls fromcollapsing, when the antenna is subjected to high impact. The dielectricmaterial serves to keep foreign matter out of the antenna and enablesthe construction of an antenna of reduced size.

ORIGIN OF INVENTION The invention described herein was made in theperformance of work under a NASA contract and is subject to theprovisions of Section 305 of the National Aeronautics and Space Act of1958, Public Law 85-568 (72 Stat. 435; 42 U.S.C. 2457).

BACKGROUND OF THE INVENTION Field of the invention This inventiongenerally relates to energy-radiating detvices and, more particularly,to an antenna capable of withstanding high impact.

Description of the prior art The exploration of space has led to thedesign and development of a large number of instruments and systems,which are capable of operating satisfactorily under space conditions.Many instruments and systems have been developed which can withstandhigh impact of a magnitude, which may be encountered when instrumentshard land on the moon, or other bodies in space. Since the success ofany space exploration mission is dependent on the ability to communicatewith the systems aboard a vehicle in space, considerable effort has beendirected to the development of antennas, through which signals may bereceived from and transmitted to earth.

Among the desired characteristics of an antenna which has to withstand ahigh impact are simplicity of design, high radiating efficiency, smallsize, high power, broad bandwidth, adaptability to provide a desiredenergy polarization, and beam shape. Additional desirablecharacteristics are light weight and satisfactory operation at hightemperatures. Although some, presently known antennas, may possess someof these features, they have been found wanting, particularly inapplications intended to survive high impact. High impact is intended tomean indirect impact in the range of 10,000g and direct impact in therange of 250 ft./ sec. of impact velocity.

OBJECTS AND SUMMARY OF THE INVENTION It is a primary object of thisinvention to provide a new improved antenna.

Another object of this invention is to provide an antenna which hassubstantially all the aforementioned characteristics.

3,534,376 Patented Oct. 13, 1970 "ice Yet another object of theinvention is to provide a new high impact antenna.

A further object of the invention is the provision of an antenna of arelatively simple, though basic design. The specific dimensions of theantenna are chosen to provide desired energy polarization and beam shapecharacteristics.

Still a further object of this invention is to provide a small, simple,highly adaptable antenna which is capable of withstanding a high impact.

These and other objects of the invention are achieved by providing anantenna which in one embodiment consists of a rectangular metallic cup,excited by a conductive probe. The cup is closed or shortened at one endand open at the opposite end, which defines an antenna radiatingaperture. The probe is slanted between two opposite walls of the cup sothat when signals are supplied thereto, the probe excites the orthogonalrectangular modes TE and TE By properly selecting the cups dimensions,including its cross-section and depth, the probe size and its locationand angle of inclination within the cup, hereafter referred to as theprobes position, orthogonal waves of selected amplitudes and phasevelocities may be excited. Consequently, at the cups open end, whichdefines the antennas radiating aperture, the amplitude of the waves andtheir phase relationship are such that radiation of a selectedpolarization and in the form of a beam of selected shape are obtained.

For example, by choosing a cup with a selected rec tangularcross-section and by controlling its depth and the proper positioning ofthe probe, the two orthogonal waves which are excited may become equalin amplitude and in phase quadrature at the aperture, so that circularlypolarized radiation is achieved. If the cups cross-section is chosen tobe square, the proper amplitude and phase relationship of the two waves,at the aperture, may be obtained by the use of suitable perturbations.

In addition to the probe which is supported in the cup, the latter ispreferably filled with a dielectric material. Its function is to securethe probes position in the cup when subjected to high impact, as well asto strengthen the cups side walls so as to minimize their distortion dueto the impact. It is appreciated that when dielectric material fills thecup it keeps foreign matter out of it. Also, due to dielectric loading,a cup of reduced size may be utilized, thus resulting in a smaller sizeantenna.

The novel features that are considered characteristic of this inventionare set forth with particularity in the appended claims. The inventionwill best be understood from the following description when read inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an isometric view of oneembodiment of the present invention;

FIGS. 2, 3 and 4 are three mutually perpendicular views of theembodiment of FIG. 1, with FIG. 2 representing the front view;

FIG. 5 is a diagram of radiation patterns of an antenna constructed inaccordance with the teachings of the invention, recorded before andafter high impact;

FIG. 6 is an isometric view of another embodiment of the invention; and

FIG. 7 is an isometric view of still another embodiment of the inventionconsisting of a cup antenna with a circular cross-section.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference is now made to FIG. 1which is an isometric view of one embodiment of a cup antenna,constructed in accordance with the teachings of the present invention.

Dielectric material, which is practice fills the cup, is purposelydeleted in order to diagram various internal parts of the antenna. FIGS.2, 3 and 4 are respective front and two side views of the sameembodiment. The antenna consists of a ruggedized metallic cup 10, havinga substantially square cross-section with a closed or shorted bottom endand an opposite open end. The open end defines the radiating aperture ofthe antenna.

A coaxial connector 12 is supported at the bottom end of the cup. Thecenter conductor of the connector is electrically coupled to a probe 14which is supported in the proper position within the cup by a probesection 15. Hereafter however, whenever the probe is mentioned it refersto the section, designated by numeral 14.

The probe 14, which may take the form of a dipole, a loop, or any otherconfiguration, hereafter all referred to as probe, is supported so as toslant between two opposite side walls of the cup, such as walls a and10b, at a predetermined selected distance from the bottom end of the cupand preferably parallel thereto. By supplying energy to the probe, dueto its slanted position and the shape of the cup 10, it excites therectangular modes TE and TE perpendicular to one another. Due to theequal dimensions of the sides of cup 10, i.e., since the cup is ofsquare cross-section, the two modes will propagate with the same phasevelocity. To introduce differential phase between the modes, in order toproduce radiation in a selected polarization, the presently describedembodiment of the invention includes a pair of perturbations, designated16 and 17, respectively positioned on the opposite sides or walls 10aand 10b of the cup. These two perturbations are in the form of angularridges.

As is appreciated by those familiar with the art, by properly selectingthe cups dimensions, including its depth and cross-section, thedimensions and shapes of the perturbations, the probe size and itsposition, the two modes excited thereby may be made to be at a desiredamplitude and phase relationship at the aperture of the cup.Consequently, energy which radiates at a selected polarization may beobtained. For example, the various dimensions and positions may beselected so that the two orthogonally excited modes are equal inamplitude and in phase quadrature at the aperture, so that the energyradiating out of the open end of the cup, i.e., the antennas radiatingaperture, is circularly polarized.

As previously remarked, in order to enable the antenna to sustain highimpacts, the cup is filled with a dielectric material 20 (FIG. 2). Itsfunction is to secure the position of the probe 14 within the cupdespite the high impact, as well as to help prevent the cup walls fromdistorting or collapsing during the impact. In addition, it serves tokeep any foreign matter from entering the cup and thereby distort itscharacteristics. The dielectric material is chosen to have highcompressive strength, low electric losses, and good performancecharacteristics at high temperature. For

, antenna applications in a vacuum, it is preferred that the dielectricmaterial also have low outgassing characteristics. In addition, thechosen dielectric material should have a reasonably high dielectricconstant so that the overall size of the antenna can be reduced, due tothe dielectric loading produced by the material.

Dielectric materials which have been found to be quite satisfactoryinclude Eccofoam PT, and Stycast 1090, all of which are manufactured andsold by Emerson and Cuming, Inc., of Canton, Mass. Other materials whichhave been found useful include fused silica and Imidite SA, the lattersold by Whittaker Corporation. It should be pointed out that thesematerials exhibit different characteristics and therefore the particularmaterial which is selected would depend on the particular conditionswhich the antenna may be subjected to. Also, it should be apparent thatother dielectric materials may be used, and therefore the enumeratedmaterials should be regarded as exemplary only.

In one specific embodiment which was actually reduced to practice, theantenna was designed to radiate energy at 2298.3 mHz. The antenna cup ofmetallic material was square, with internal dimensions of 2.1 by 2.1inches and 2.2 inches. A probe of 0.093 inch in diameter was supportedwithin the cup at an inclination of The probe length was 1.368 inchesmeasured from the center of section 15 and its center was spaced 1.740inches from the bottom of the cup.

Two triangular ridges were centrally positioned within the cup onopposite side walls, such as 10a and 10b. The base of each ridge was0.583 inch, while its height was 0.535 with the front sides of theridges sloped at a angle, as diagrammed in FIG. 3. The ridges 16 and 17were purposely used to provide circularly polarized radiation. Thedielectric material was Eccofoam PT. The radiation patterns measuredbefore and after an indirect impact of 10,000 g over a duration of 0.6millisecond are diagrammed in FIG. 5 to which reference is made herein.As seen from the figure, impact did not produce any appreciable changein the electrical performance of the antenna.

In addition to the high impact characteristics of the antenna of thepresent invention, other of its desirable characteristics include itssmall size, partly accountable by the dielectric loading, provided bydielectric material 20, its simple construction, and light weight,relatively broad bandwidth, and its adaptability to radiation of energyat selected polarization. The latter feature is accomplished bycontrolling the cups dimensions, its perturbations, the probe size, andits position. Also, since the antennas radiating aperture is defined bythe open end of the cup, the antenna has a relatively large aperturefavoring high power operation, which is enhanced by placing theconnector at the cups corner where the field is relatively small. Thelarge aperture minimizes the danger that the antennas aperture may beclosed by a high impact.

It should further be pointed out that when utilizing the embodiment inwhich the antenna cup has a square crosssection, the shape of theradiating beam is substantially equal in all directions about thelongitudinal axis of the antenna. This feature may be particularlydesirable when the final orientation of the antenna with respect to areceiver or transmitter is not known. In some applications, however, itmay be desirable to produce radiation of unequal beam width. In such acase, a cup of rectangular cross-section, may be employed. An isometricview of an antenna, employing such a cup, is shown in FIG. 6, to whichreference is made herein. Therein, the cup is designated by numeral 30,the dielectrical material by numeral 32, and adjacent side walls ofdifferent lengths by 33 and 34. In such an arrangement, if circularpolarized radiation is required, the cross-sectional dimensions of thecup, as well as its depth, are controlled to produce phase quadraturebetween the two modes at the aperture, without resort to perturbationsor ridges, such as those shown in FIG. 1. That is, the dimensions of therectangular cross-section, the depth of the cup, probes position with inthe cup and the dielectric material are selected to provide twoorthogonal modes which are equal in amplitude and in phase quadrature atthe aperture, which defines the antennas radiating aperture, to producecircularly polarized radiation.

Due to the high impact characteristics of the novel antenna of thepresent invention, the antenna can be used advantageously in spaceexploration where hard landing of instruments is planned orcontemplated. In addition, the antenna may be utilized, in conjunctionwith a transmitter designed to survive very high impact, as a searchbeacon antenna for aircraft. The combination of such a transmitter withthe novel antenna of the present invention would be most advantageous inlocating the site of a downed aircraft. The antenna may similarly beused aboard ship, since the dielectric material 20, which fills the cup,would serve as a filling material to minimize the adverse effect ofmoisture or ship vibration on the antennas operation.

In another embodiment of the invention, the cup antenna may be ofcircular cross-section, as shown in FIG. 7, to which reference is madeherein. In FIG. 7, the di electric material is purposely deleted inorder to show two internal ridges 41 and 42, and a probe 45. Since acircular cup antenna is symmetrical about its longitudinal axis, itsstructure may be found to be more advantageous in certain applications,such as in a high pressure environment or when dictated by spacerestrictions. In FIG. 7, the two ridges are shown extending along thecups inside wall. The probe 45 is inclined at 45 with the plane ofsymmetry. The probe excites the dominant TE mode in the cup. This modemay be considered as a superposition of two, approximately equalamplitude, orthogonal TE modes, one perpendicular and the other parallelwith the plane of symmetry. The function of the ridges is to introduceappropriate phase shift between this mode pair for circularpolarization.

There has accordingly been shown and described herein a novel highimpact antenna, consisting primarily of a cup of a preselectedcross-sectional configuration and dimension. One end of the cup isclosed or shorted and the other end is open, acting as the antennasradiating aperture. By controlling the depth of the cup, and theposition of a probe within the cup, radiation of a selected polarizationmay be obtained with or without the use of perturbations as may berequired. By filling the cup with dielectric material of selectedproperties, the cup size is reduced and the probe is secured within itto withstand high impact, as well as to support the cups side walls fromdistortion during the impact. The probe may be replaced by a dipoleantenna or loop or any other means, designed to excite two orthogonalelectromagnetic waves within the cup, which, as a function of theiramplitudes and phase relationship at the cups aperture, produce thedesired polarization and pattern of the radiated energy.

It is appreciated that those familiar with the art may makemodifications and/or substitute equivalents in the arrangements asshown. Therefore, all such modifications and/or equivalents are deemedto fall within the scope of the invention as claimed in the appendedclaims.

What is claimed is:

1. An antenna comprising:

a cup-like member having one shorted end perpendicular to a longitudinalaxis of said member, and an opposite parallel open end, said open endserving as an antenna radiating aperture, said member having across-section of a preselected geometric configuration in a planeperpendicular to said longitudinal axis;

a probe, positioned in said cup-like member at a preselected distancefrom said shorted end and in a preselected orientation;

means coupled to said probe to supply it with signals so as to exciteelectromagnetic waves of predetermined modes in said cup-like member;and

a dielectric material filling said cup, the geometric configuration ofsaid member being a square, and said probe being positioned parallelsaid shorted end and slanted between opposite walls of said cup-likemember, said walls extending from said shorted end to the open end.

2. The antenna as recited in claim 1 further including at least a firstperturbation positioned in said member to control the amplitudes andphase relationship of electromagnetic waves at the open end thereof.

3. The antenna as recited in claim 2 wherein the waves excited in saidcup-like member are in modes TE and TE and said at least firstperturbation controls the phase and amplitudes thereof to radiatecircularly polarized electromagnetic energy.

4. The antenna as recited in claim 3 wherein said dielectric materialhas a relatively high compressive strength to increase the membersability to withstand a relatively high impact with minimal deformation.

5. The antenna as recited in claim 3 wherein said antenna includes asecond perturbation, positioned opposite said first perturbation.

6. The antenna as recited in claim 1 wherein said geometricconfiguration is a rectangle and said probe is positioned parallel saidshorted end and slanted between opposite walls of said cup-like member,said walls extending from said shorted end to the open end.

7. The antenna as recited in claim 6 wherein the waves excited in saidcup-like member are the rectangular modes TE and TE and thecross-sectional dimensions of said cup, its depth, the position of theprobe and the dielectric material are selected to produce radiation ofenergy of a preselected polarization.

8. The antenna as recited in claim 7 wherein said dielectric materialhas a relatively high compressive strength to increase the membersability to withstand a relatively high impact with minimal deformation.

9. An antenna comprising:

a cup-like member having one shorted end perpendicular to a longitudinalaxis of said member, and an opposite parallel open end, said open endserving as an antenna radiating aperture, said member having a circularcross-section in a plane perpendicular to said longitudinal axis;

a probe, positioned in said cup-like member at a preselected distancefrom said shorted end and in a preselected orientation;

means coupled to said probe to supply it with signals so as to exciteelectromagnetic waves of preselected modes in said cup-like member;

first and second ridges in said member to control the relativeamplitudes and the phase relationships of the modes excited therein; and

a dielectric material filling said member.

10. The antenna as recited in claim 9 wherein said first and secondridges control the relative amplitudes and the phase relationship at theopen end of said member of two orthogonal modes TE excited therein, toproduce radiation at a selected polarization.

References Cited UNITED STATES PATENTS 11/1957 Watson 343789 X 3/1966Kelleher 343-789 US. Cl. X.R. 343-789

